A dangerous game of brinkmanship is unfolding in the Middle East pitting Israel against Syria and its militant Shi‘ite ally Hizballah in what threatens to expand the two-year Syrian civil war into a full-blown regional conflict. On three separate occasions since January — two of them within 48 hours of each other last Friday and Sunday — Israeli jets have attacked Syrian military bases, targeting consignments of advanced weaponry supplied allegedly by Iran that were pending transfer to Hizballah across the nearby border with Lebanon. The air raids were unprecedented. Israel has never before risked striking at Hizballah’s Iranian-supplied weapons inside Syria.

For now, though, Israel’s gamble seems to have paid off. Other than some initial huffing and puffing from Damascus, no immediate retaliation was forthcoming. But rather than acting as a deterrence, the air strikes appear to have galvanized Syria to promise even greater amounts of sophisticated weaponry to Hizballah and also to announce the launch of a popular resistance campaign to liberate the Golan Heights, the strategic volcanic plateau in the southwest corner of the country that has been occupied by Israel since 1967.

Israel’s intervention into the grueling Syrian civil war comes amid faint glimmers of a diplomatic breakthrough with the U.S. and Russia agreeing to an international conference to help end a conflict that has left more than 70,000 people dead. But the regime of Syrian President Bashar Assad has gained some tactical military successes of late, launching mini-offensives to retake territory previously lost to opposition rebels. The rebel setbacks may have strengthened the Assad regime’s grim resolve to win the conflict, especially given its confidence in the continued support of regional allies, Iran and Hizballah.

Certainly, the Syrian offer to supply more advanced weaponry to Hizballah has been warmly received. “This is a critical strategic decision,” said Sheik Hassan Nasrallah, Hizballah’s leader, in a televised speech Thursday evening. “We, the resistance in Lebanon, announce that we are ready to receive any sort of physical weaponry, even if it is going to disturb the [military] balance [in the Middle East],” Nasrallah added. “We are ready to receive these weapons, and we are competent enough to possess them. We will use these weapons to defend our people and our country.”

Syria’s embattled government has additionally served notice that any further air strikes by Israel will incur an immediate — albeit unspecified — retaliation. “The instruction has been made to respond immediately to any new Israeli attack without [additional] instruction from any higher leadership and our retaliation will be strong and painful against Israel,” Faisal Miqdad, Syria’s Deputy Foreign Minister, told Agence France-Presse in an interview Thursday. His comments echo previous reports this week in Syrian media loyal to the Assad regime that missile batteries will be able to respond to another Israeli air attack.

And Hizballah sources say they, too, have received similar instructions. “From that night [Sunday] to this day, we haven’t slept a wink. If there’s another air strike, if the Israelis hit Lebanon or Syria, we’ll retaliate immediately,” Abu Khalil, a veteran Hizballah combatant told TIME, giving his nom de guerre as he was not authorized to talk to the media. “We are ready and the Syrians are ready,” he added, speaking Wednesday before Nasrallah’s speech. Abu Khalil’s colleague Haj Hassan, another combat veteran, doubted that Israel would risk another air strike in the near future. “They can’t do it. Can you hold four watermelons in one hand?” he asked, meaning that a fourth air strike would prove too much of a burden for Israel because of the backlash.

Nevertheless, there are no indications that Israel intends to suspend the air strikes against weapons systems it considers “game changers” in the context of the Israel-Hizballah conflict. Israel appears to calculate that the Assad regime cannot afford to retaliate while fighting for its survival against opposition rebel forces. Similarly, Hizballah is busy deploying fighters into Syria to help the Assad regime crush the rebel factions in what has fast turned into a brutal sectarian war. Hizballah has shown no interest in resuming direct hostilities with Israel since the end of a monthlong war in July-August 2006, when the group’s crack fighters fought the Israeli army to a standstill in the battlefields of south Lebanon.

The sophistication of the weaponry allegedly being transferred to Hizballah today underlines not only Israeli concerns but also the huge expansion of the group’s military capabilities over the past two decades. Twenty years ago, the largest rocket facing Israel from Lebanon was the 122-mm Katyusha with a range of about 12 miles, just far enough to cross Israel’s then-occupied border strip in south Lebanon and threaten a narrow ribbon of northern Israel. Since then, the Israelis have watched as Hizballah’s rocket arsenal has grown in size and quality: first came Iranian 240-mm Fajr-3 and 333-mm Fajr-5 rockets, which placed Haifa, 25 miles south of the Lebanese border, within range for the first time. Then came Syrian 220-mm and 302-mm rockets followed by the Iranian 600-mm Zelzal-1 and Zelzal-2s, the latter possessing a range of some 125 miles.

Israeli officials wrung their hands amid the buildup, unwilling to risk a war by attacking the arms depots in Syria or convoys moving into Lebanon. Instead they called for international pressure to check the flow of arms and regularly aired their assessments of Hizballah’s latest rocket tallies: 8,000 in 2000, rising to 10,000 two years later and 13,000 on the eve of war in 2006.

Hizballah’s military clout has helped ensure that the party remains the dominant political and military force in Lebanon. It insists that its formidable military might is necessary to defend Lebanon against future Israeli aggression, a justification that wins little sympathy from Hizballah’s critics, who fear the influence the party’s weapons bring to bear on the domestic scene.

Hizballah typically refuses to disclose details of its arsenal. But the organization does not disguise the fact that it has amassed a significant stockpile of advanced weapons, and today its leaders boast that no place in Israel is beyond its reach. “We don’t fight our enemies with swords of wood,” quipped Nasrallah in 2007.

Since the 2006 war, Hizballah’s armaments have expanded even further in quantity and sophistication. Israeli officials claim the Shi‘ite party has acquired anything from 60,000 to 80,000 rockets. In 2009, reports emerged that Hizballah had received M600 missiles, a Syrian-engineered version of Iran’s Fateh-110 with a guidance system that allowed it to strike within 500 yards of its target at its maximum range of about 150 miles. A few months later in 2010, Western and Israeli intelligence sources were alleging that Scud ballistic missiles had been transferred to Hizballah’s care, although it was unclear whether the missiles had been smuggled into Lebanon or remained housed in Syrian military bases close to the Lebanese border.

The target of Israeli air strikes on Friday and Sunday appears to have included upgraded versions of Iran’s Fateh-110s with slightly longer range and improved accuracy over the Syrian M600s.

Smuggling rockets nudging 30 ft. in length across Syria’s closely scrutinized border with Lebanon is a skill in itself. The arms convoys tend to follow dirt tracks that snake across the remote rugged mountains marking the border. They roll in at night and when possible use poor weather to mask their movements. According to sources close to Hizballah, the party’s engineers sometimes cut the local electricity supply and jam cell-phone and radio signals when the convoys are on the move.

Israel is so concerned at Hizballah’s acquisition of advanced arms that the rate of Israeli reconnaissance flights above Lebanon since the beginning of the year is roughly double that of the same time in 2012, according to sources with the U.N. peacekeeping force in south Lebanon, which uses ground and ship-borne radars to track the overflights. The rumble of Israeli jets can be heard above Beirut on a near daily basis, their white contrails crisscrossing the blue skies.

Hizballah proved in the 2006 war that it possesses top-range Russian antitank missiles, which were employed to deadly effect against Israel’s fleet of Merkava tanks and in one instance to bring down a troop-transport helicopter as it was taking off, killing the five-man crew. The group also came close to sinking an Israeli naval vessel with an Iranian antiship missile. But its air-defense capabilities remain something of a mystery — for now. Some analysts speculate that Nasrallah’s frequent reference to military “surprises” in store for Israel in the next conflict will be the unveiling of advanced antiaircraft capabilities to dent Israel’s vital aerial dominance over Lebanon. “In the [2006] war, we showed the Israelis that they cannot use the sea. They used their helicopters and we took them out. They used their best tanks and we slaughtered them,” said Abu Khalil. “We have orders to keep the skies open for them for now. But when that order changes, you will see what is our next surprise.”

The Israeli jets that attacked the Syrian military bases on the past three occasions launched their long-range missiles from high altitude in Lebanese airspace 10 miles or more from their targets to lower the risk posed by Syria’s dense array of antiaircraft batteries in the Damascus area. But if the attacks against Hizballah’s arms caches in Syria continue, the Israeli air crews could suddenly find that Lebanese airspace has become equally as dangerous.